How to stop excessive sweating?!

Switch to a clinical strength deodorant.

Best deodorants for men:
Gilette Clinical Strength Ultra Comfort
Odor Shield Clinical Strength Gilette

Best deodorants for women:
Secret Clinical Strength Waterproof
Dove Clinical Protection
Arrid Clinical Strength

Wear all cotton clothing, especially undergarments. Stay away from wool, fleece, polyester, and other synthetic fabrics that can make you sweat more. If you are still sweating excessively, talk to your doctor about it.

Of course it doesn't help. Deodorant doesn't stop sweating it just prevents the sweat from smelling. Antiperspirant is what prevents sweating, but even the over the counter ones suck. If you sweat a lot just go to the doctor and ask him for a prescription antiperspirant. They work great. I'm allergic to deodorant so I use the antiperspirant and I only have to apply it like once every 10 days and I'm good.

-Connor

Shay's answer could be a contributing factor if you are over weight. It just may be your metabolism (hope I spelled that right) to sweat a great deal. I really think a call to your doctor may be in order. Tell the receptionist you would likeher/him to ask the doctor if your excessive sweating needs an appointment. If yes then of course see your doctor.
My personal opinion for what its worth is I don't like putting something on my underarms to prevent my sweat glands from working. I therefore shave my armpits, especially since I were dress shirts in my job. I also use a less toxic solution occasionally like Toms deodorant.

Make sure it is an "antiperspirant" and "deodorant", if it is just the deodorant, then that is only covering the smell.

Good luck

Old enough to know

Losing a lot of weight will help and exercising frequently.

Might be your diet, or drinking a lot of coffee